AN-2602: Innovative Power Management Solutions: Efficient, Reliable, and High Performance in a Compact Design

Introduction

Ensuring efficient, reliable, and high-performance power supply is crucial for system performance and reliability in today's communication devices, data centers, industrial automation, medical equipment, and artificial intelligence fields. In the realm of communication devices, especially in infrastructure and network equipment, the efficient power supply is vital for continuous communication and data processing. Common applications like optical modules require power management components with efficient energy conversion, dynamic adjustment capabilities, and the ability to operate in space-constrained environments to ensure system reliability and communication quality. Similarly, to meet rising workloads from 5G, social networks, media, and cloud computing, data centers must achieve high energy efficiency and low heat/power dissipation for high-density servers and storage devices in the smallest form factor. The rapid advancement of artificial intelligence technology also drives the need for high-performance power management solutions. With the growing demand for cloud computing, AI applications, and high-power processors and accelerators, minimizing board space, meeting stringent dynamic requirements, and expediting the development cycle from concept to final product have become significant challenges.

To address these demands, the LT7170, a member of Analog Devices’ digital power system management (DPSM) family, emerges as a solution. This monolithic DC/DC synchronous step-down regulator integrates DPSM technology, offering dynamic configuration and monitoring through a PMBus/SMBus/I²C digital interface. DPSM features include digital monitoring of voltage, current, power, and temperature; on-the-fly adjustment of configuration parameters; trimming, margining, sequencing, and supervision of multiple point-of-load supplies; as well as remote supervision and command of the power system.

The LT7170 seamlessly combines Silent Switcher® technology with state-of-the-art PMBus control and telemetry, positioning it as Analog Devices’ "Smart Silent Switcher®" product. The Silent Switcher® architecture ensures exceptional efficiency at high switching frequencies while emitting ultra-low electromagnetic interference (EMI), resulting in compact and quiet step-down solutions. By integrating Silent Switcher® technology with advanced PMBus control, the LT7170 significantly reduces solution size and external component count, while simultaneously improving efficiency, output voltage accuracy, EMI, and load transient response performance. The LT7170, a 16V, 20A monolithic buck regulator, is an ideal candidate for high-current, space-constrained, and noise-sensitive applications, offering the feature-rich versatility of DPSM.

Digital Power System Management (DPSM) Features

Applications such as artificial intelligence, machine learning, content streaming, remote collaboration and learning, and cloud-based services are driving the rapid growth of data center servers, telecom systems, and networking equipment. The key to reducing energy consumption in these areas lies in improving power conversion efficiencies. Solutions are needed that enhance efficiency and address the complex power requirements of processors, application-specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs), providing higher power density to fit into smaller footprints without compromising speed or reliability, while offering industry-leading design efficiency. To address the challenges of active power management and space constraints, solutions based on the PMBus feature are highly effective, providing a platform for monitoring and controlling power management devices with a minimal number of components.

Figure 1 illustrates a typical power system architecture used in data center servers. It starts with an AC-DC converter that transforms AC power into 48V DC. The 48V power goes through a 48V hot swap module, followed by a 48V to 12V DC-DC converter to step down the voltage to 12V. This 12V voltage is subsequently distributed to various point-of-load (PoL) converters on the board, which then deliver power to the ICs or sub-circuits, such as ASIC, FPGA, CORE, DDR, I/O, and system bias. Most of these ICs or sub-circuits operate at voltages ranging from a few hundred millivolts to 3.3V. These power rails require precise sequencing, monitoring, voltage accuracy, and supervision. In complex systems with dozens of voltage rails, proper power-up and power-down sequencing is essential for each PoL voltage rail. PMBus technology offers a flexible and robust digital power management protocol, enabling remote control and monitoring of power supplies, thus meeting these requirements effectively.

Figure 1. Typical power distribution structure in data center servers.

The LT7170 is a member of Analog Devices’ DPSM family. So, it can be configured and monitored through a PMBus/SMBus/I²C digital interface or stored in the on-chip, three-times programmable nonvolatile memory (NVM). As shown in Figure 2, the LT7170 includes several power system management (PSM) functions, including programmable parameters, accurate telemetry readback, and fast programmable fault response, which make it versatile and flexible. It features wide input and output ranges, and is highly customizable through PMBus. The following parameters of the LT7170 are configurable and storable through the I²C/PMBus interface:

Figure 2. LT7170 configured and monitored through PMBus/I²C interface.

Output voltage, overvoltage, undervoltage, and current limit
Digital soft-start/stop, sequencing, and margining
On and off delay times and output rise/fall times
OV/UV thresholds
Control loop compensation
Switching frequency
Output voltage transition rate
Switch slew rate for EMI and efficiency optimization
Fault response

Additionally, PMBus functionalities enable the monitoring of power supply operation, covering:

Input and output voltage
Output current
Internal die temperature
Switching frequency
Part, system, and fault status

Figure 3 displays a screen from LTpowerPlay, a robust Windows-based software development tool featuring a graphical user interface (GUI) tailored to fully support the LT7170. LTpowerPlay offers unparalleled capabilities for development, diagnostics, and debugging. Through the GUI, telemetry, system fault status, and PMBus command values are readily accessible. For instance, within the red dashed box in Figure 3, control loop compensation, V_OUT, OV/UV settings, and V_OUT transition rate of the LT7170 can be programmed through PMBus. Similarly, within the yellow dashed box, telemetry readback parameters, including V_IN, V_OUT, I_OUT, and die temperature are available. LTpowerPlay can significantly enhance the design process by facilitating component selection, system optimization, and troubleshooting, allowing engineers to quickly make adjustments, debug problems, and find solutions, ultimately shortening design time and accelerating the development cycle.

Figure 4 shows a telemetry plot example depicting the ramping up of V_OUT from 0.8V to 1.2V, with the V_OUT transition rate set to 0.1V/ms using LTpowerPlay. The telemetry plot clearly shows that V_OUT linearly increases from 0.8V to 1.2V, and this is also verified by the oscilloscope waveform, which confirms that V_OUT jumps from 0.8V to 1.2V with a 0.1V/ms transition rate.

Figure 4b. Oscilloscope waveform of V_OUT jumps from 0.8V to 1.2V with 0.1V/ms V_OUT transition rate.

High Current, High Efficiency Fits Tight Space

Integrated MOSFETs, built-in feedback resistors, and compensation circuitry all simplify the system design and minimize total solution size with circuitry simplicity and the Silent Switcher® architecture.

Thanks to high-performance power conversion, the LT7170 delivers high current without the need for additional heat sinks or airflow. Only a few external components are required to create a wide selection of high-current, low-profile converter solutions with the LT7170. The LT7170-1 option has two switching phases connected to two inductors to drive a single regulated output supply. Figure 5 illustrates a 1V/20A LT7170 solution using a 160nH inductor and a 1V/20A LT7170-1 solution using two small 400nH inductors switching at 1MHz with all ceramic capacitors in a very low-profile solution, making this part particularly suitable for applications where board space or component height is limited.

Figure 5a. LT7170 1V/20A 1MHz solution size.

Figure 5b. LT7170-1 1V/20A 1MHz solution size.

The Silent Switcher® architecture produces fast and clean switching edges, reducing switching losses. Minimal switching losses, along with just 25ns of minimum on-time, enable high efficiency at high switching frequency and a small solution size. The input range for the LT7170 is 1.5V to 26V with EXTV_CC. Figure 6 illustrates a typical application of the LT7170-1 for a 12V input to 1V/20A with a 1MHz switching frequency power supply solution that uses two small 400nH inductors and ceramic capacitors in a very low-profile solution for FPGA or microprocessor applications. The efficiency for this circuit can reach as high as 91%, as depicted in Figure 8. Figure 7 shows the thermal performance of this circuit running at 15A without heat sinks or airflow. The IC case temperature rise is 44.2ºC, where the ambient temperature is 25ºC.

Figure 6. LT7170-1-based 12V to 1V synchronous step-down converter with PMBus/I²C control and monitoring interface.

Figure 7. LT7170-1 thermal image for 12V input to 1V output at 15A with f_SW = 1MHz, no airflow, T_A = 25ºC.

Figure 8. Efficiency of the 12V_IN to 0.8V_OUT, 1V_OUT, 1.8V_OUT at 1MHz.

Figure 8 shows the efficiency of a 12V input voltage to various output voltages, such as 0.8V, 1V, and 1.8V, at a switching frequency of 1MHz, with applications in providing power supply for ASICs, FPGAs, and I/O, as shown in Figure 1.

Silent Switcher® with Excellent EMI Performance

The Silent Switcher® architecture effectively counteracts EMI by incorporating built-in hot loop capacitors, thereby reducing the size of the disruptive antenna. This, paired with integrated MOSFETs, substantially diminishes switching node ringing and associated energy stored in the hot loop, even during rapid switching transitions. This results in outstanding EMI performance while concurrently minimizing AC switching losses. Silent Switcher® technology is incorporated in LT7170 to minimize EMI and deliver, which greatly simplifies EMI filter design and layout, making it an ideal choice for noise-sensitive environments.

Figure 10 illustrates the CISPR32 Class B radiated EMI performance of a 1MHz LT7170-1 application circuit, which converts a 12V input to a 1V/20A output with only a ferrite bead applied at the input, as depicted in Figure 9. The LT7170-1 effortlessly complies with the CISPR32 Class B radiated EMI specification with a significant margin, even without an EMI filter. For applications in noise-sensitive environments, such as data centers, solid-state drives (SSDs), industrial systems, and communication equipment, additional EMI suppression can be achieved by adding two 10µF ceramic capacitors (as indicated by the dashed lines in the diagram) on both sides of the ferrite bead, significantly reducing EMI noise in the 500MHz to 800MHz range.

Figure 9. Ultralow EMI emission, LT7170-1 12V input to 1V/20A output with f_SW = 1MHz.

Figure 10a. CISPR 32 Class B radiated EMI performance for the circuit in Figure 9, with only a ferrite bead.

Figure 10b. CISPR 32 Class B radiated EMI performance for the circuit in Figure 9, with a ferrite bead and two ceramic capacitors at the input.

High Performance Load Transient Response

The LT7170 offers programmable loop compensation to assure loop stability and optimize the transient response of the controller without any external component changes. With just a few clicks of a mouse using LTpowerPlay, the LT7170 can achieve optimal compensation. The control loop is fine-tunable quickly and painlessly, regardless of last-minute component substitutions or variations. This empowers designers to squeeze the maximum performance out of their systems by removing unnecessary output capacitors while saving board space and cost. Figure 3 demonstrates the error amplifier gm, current limit, compensation resistor R_ITH, and capacitor C_ITH can be programmed in LTpowerPlay.

To support high step-down ratios and fast load transient response, the LT7170 uses controlled on-time valley current-mode control with a typical minimum on-time of 25ns. Figure 11 shows the typical waveforms of LT7170- 1 for a 12V input to 1V output with a 10A load step transient at 1MHz, resulting in only a ±1.7% deviation from nominal.

Figure 11. LT7170-1 load transient performance for a 10A load step.

Conclusion

In summary, the LT7170 with DPSM technology stands out as an innovative power management solution, catering to a wide array of applications such as communications, data centers, storage, and industrial systems. Its integration of Silent Switcher® technology with PMBus control and telemetry ensures efficient, reliable, and high-performance power delivery in compact designs. Additionally, the LT7170 offers excellent EMI suppression, making it ideal for noise-sensitive environments, and features fast load transient response, ensuring reliability under dynamic conditions. Leveraging LTpowerPlay can significantly enhance the design process by facilitating component selection, system optimization, and troubleshooting. This robust tool allows engineers to quickly make adjustments, debug problems, and find solutions, ultimately shortening the design time and accelerating the development cycle. Overall, the LT7170 provides a comprehensive and highly effective solution for modern power management challenges.